That would be me. I have built a set for my Nacra's and have mounted the first on my Nacra 5.7. The design will work on any CAT with 4" round cross beams that don't have the traveler track extending over the hull portion of the beam. I have to work on mounts for other shapes but don't think it will be a problem.
The first real production prototype worked out well on our trip to Tahoe and the most recent trip to Mission Bay. All my non sailors commented on how much better sailing on the CAT was with them since they didn't have to sit on the tramp and try to stay out of the way off all the sheets. I actually enjoyed using them quite a bit too. They are incredibly easy to remove or fold up for trailer'n, but I never ended up removing, and was able to fly the hulls quite high with out issue.
I plan to build and sell these, but my main business of manufacturing cartridges and systems to take oil out of water has been booming as of late and left little time for focusing on something new. I've kind of resigned myself to the fact that this will end up being a winter project with the plan to make available for next season. I would like to get my hands on some of the newer CATS with the 'D' beams so I can design the mounts for those.
John, I hadn't talked to Brett Johnson (azcat) after the Tripoint race, so emailed him. " I beat Lee (Wickland) by welding a whole bunch of extra aluminum to his boat". Pete
The seats that I'm building don't fit inside the beams like those you have. But you should be able to make a mold and cast some fittings, or even better, get some PVC or Delrin stock that is 4" OD and have a machine shop turn down, notch for the bolt rope area in the beam, then drill a hole down the middle to receive your current seats.